Wind energy is an attractive alternative to fossil fuels because it is plentiful, renewable, widely distributed, clean, and produces no greenhouse gas emissions. In order to maximize electrical generation, wind turbines are typically sited in high-wind areas such as mountainsides and canyons. Wind turbines are also sited offshore, to harness strong coastal winds.
The wind harnessed for power generation can also damage a turbine, however. While stronger winds generate more power, high and fast wind speed and direction change, e.g. extreme gusts, may generate tremendous stress on the components of the turbine. In particular, blades, hubs, and gearboxes are vulnerable to stress-related failure. By advanced materials and precision engineering, large, modern turbines can achieve reliable performance in wind speeds up to 30 m/s. Nonetheless, every wind turbine has a cut-out wind speed above which the turbine cannot safely operate for extended periods. If the speed of the wind substantially exceeds the cut-out wind speed while the turbine is producing, the turbine can lose its capability to control shaft torque and/or running speed and can be damaged, resulting in downtime and costly repairs. Also when the operating turbine is reached by an extreme gust, the turbine can be damaged if its control system doesn't respond promptly to bring it to shut down.
For example in the event of very rapid variation of wind speed and or wind direction (specifically in the case of the extreme coherent gust with wind direction change or other extreme gusts), the safe limits of rotor aerodynamic torque and speed can be exceeded, even after the control system starts the shut down (when based on shaft over-speed sensor). This can result in dangerous stresses on the blades, hub, drive train, and other subsystems—all of which can result in turbine failure.
To avoid damage in high winds, many wind turbines have rotor speed sensors which sense the speed of the rotor shaft, for example, through a speed pick-up, which is used for power control and for shutdown. In such wind turbines, a braking system is activated in the event of shaft over-speed. The response of the running speed lags the variation of the aerodynamic torque, however, because of the inertia of the rotor. Thus, the corrective action is not initiated until well after the onset of the wind event.
Thus, there is a need for a control system that can instantaneously sense rapid variations in wind speed seen by the rotor and initiate corrective action.